Considerable difficulty has been experienced in locating leaks of liquids and, in particular, hydrocarbon liquids such as crude oil, from submerged pipelines, especially such pipelines which lay in open sea or ocean waters. Localization of the leak location is usually accomplished by searching for an oil slick on the water's surface or by seeking some other surface indication of escaping liquids. When some indication of a leak is found divers are employed to search out the exact leak site. Localization in this manner is sometimes impeded because wave action or smallness of the leak prevents surface indication of it from being spotted.
The method of the invention involves the use of sonar to locate leaks of liquids from pipelines. The principles are known and have been applied in the past to show on recordings of reflected acoustic waves the acoustic echos created by hydrocarbon gas escaping from natural seeps in the sea floor or from submerged pipelines. The present invention concerns the detection of liquids leaking from submerged pipelines. The detection function is predicated on the difference in acoustic properties between seawater and the foreign liquid material, such as hydrocarbon liquids (crude oil) escaping from a submerged pipeline. Detection of the leak can be enhanced by introducing into the pipeline a substance or substances, gaseous and/or liquid, which increases the difference in acoustic impedance between seawater and the liquid escaping from the leak. The method of the invention also involves running a "base case" (no-leak conditions) sonar scan of the pipeline to provide comparison of the ocean floor during normal and leak conditions. The comparison of the "no-leak" sonar scan with a later "leak" scan of the pipeline detects the leak location by variations in the scans caused by (1) the leaking fluids themselves (2) a cavity or anomoly formed in the ocean floor by the fluids flowing from the leak in a buried pipeline; and/or (3) sediments that are dispersed by the flow of fluids from the leak. Enhancement of the leak location may be made by restricting flow from the end of the pipeline to cause increased displacement of sediments and increased excavation of a cavity due to increased flow from the leak and/or replacement of the fluids in the pipeline with "nonpolluting" material such as salt water or air and continued displacement of that material through the leak to cause growth of sediment dispersion and increased cavity size. The interface between materials having different acoustic impedances is detectable by known sonar techniques, e.g. side scan sonar, front scan sonar, or direct over-bottom sonar.